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Current across the antenna loading coil - from scratch
Another 'speriment occured to me, for those who think the coil current
MUST be different at the two ends by the amount corresponding to the antenna section it replaces: try making the antenna diameter large compared with the coil diameter, say two to four times the coil diameter, while maintaining the same lengths, and see what happens. I suppose you'll have to adjust the inductance of the coil, but keep its diameter and length the same. If the current at the ends of the coil remains nominally the same as with a thin antenna, then I'll say you're onto something. If on the other hand, the current becomes much more similar at the two ends of the coil, that will be evidence of a different effect--in fact the effect that I expect is actually accounting for the difference. Perhaps someone would like to try that in NEC2 or NEC4 and share the results, if nobody is actually up to building the antenna and measuring things. Cheers, Tom Tom, W8JI, wrote in Message-ID: .com: Yuri Blanarovich wrote: W8JI and other unbelievers that antenna and loading coils can not be expressed in electrical degrees, can find another example in ON4UN's Low Band DXing book, 4th edition, page 9-47, Fig 9-58, showing loaded vertical with mast being 40 deg. 59.6 ft. long, loading coil of 144 uH taking (replacing radiator of) 40 deg and whip of 10 deg and 14.9 ft long, for overall 90 deg electrical and quarter wave resonant system. Soooo, to anyone outside of "equal current worshippers" it is obvious that coil is replacing 40 deg worth of radiator and it would drop equivalent amount of current across the coil that corresponds to the length of radiator that coil replaces, because rest of the "straight" radiator FORCES IT TO DO - because of standing wave and current. That is not correct Yuri. Anything from a pure inductance to a very poor distributed inductor (like a linear loading or stub) can be used and all would have different characteristics. A pure inductance would have no current difference at each end. A good compact inductor would have negligible current difference at each end, only a long straight wire would act like the "missing antenna". One way to prove the coil does not replace missing length is to simply move the coil to a new location in a fixed height antenna. If the coil looked like 40 degrees, it would resonate the antenna no matter where it was installed. 73 Tom |
Current across the antenna loading coil - from scratch
Of course loading coils can be expressed in electrical degrees. But
extrapolating this to mean that a loading coil has the same properties as an antenna with the same number of "degrees" has no justification. Yuri's theory was shown to be false not only by many of the good technical arguments given here in this thread, but also by a careful measurement I made over a year ago. I built a 33 foot high vertical and loaded it at the bottom with a toroidal inductor to resonate it at 3.8 MHz. The coil "replaced" 33.4 electrical degrees of antenna. Yuri's theory predicts that the current at the top of the inductor should be 16.5% less than that at the bottom, with a phase shift of 33.4 degrees. What I measured was a current drop of 5.4% and no measurable phase shift across the inductor. Both the description of the setup and the detailed results were posted on this newsgroup on Nov. 11, 2003, with the subject title " Current in antenna loading coils controversy - new measurement". Anyone can find those postings with groups.google.com. Yuri's response, also on Nov. 11, 2003 was to complain about my methodology, declare that he was still right, and state "I will measure things myself, try to verify previous measurements and then come up with conclusions and 'theory'." On Nov. 12, 2003, he posted: "I will be making snap-on current probe, which will make it easier to slide along the element and observe the current without the disturbance to the antenna and will be a bit different over the thermocouple meters. Just need a bit more time." Well, it's been over a year now, and all I've seen is the same unsupported theory with no evidence to contradict the contrary evidence which has been presented. When a belief stays fixed in spite of both contradictory solid theory and measurements, it fits into the category of religion, not science. So it's appropriate that Yuri speaks in terms of an explanation being a "heresy". What's next, "good" and "evil" theories? Roy Lewallen, W7EL Yuri Blanarovich wrote: W8JI and other unbelievers that antenna and loading coils can not be expressed in electrical degrees, can find another example in ON4UN's Low Band DXing book, 4th edition, page 9-47, Fig 9-58, showing loaded vertical with mast being 40 deg. 59.6 ft. long, loading coil of 144 uH taking (replacing radiator of) 40 deg and whip of 10 deg and 14.9 ft long, for overall 90 deg electrical and quarter wave resonant system. Soooo, to anyone outside of "equal current worshippers" it is obvious that coil is replacing 40 deg worth of radiator and it would drop equivalent amount of current across the coil that corresponds to the length of radiator that coil replaces, because rest of the "straight" radiator FORCES IT TO DO - because of standing wave and current. Such a heresy! Theeere is your sign! Yuri, K3BU/m |
Current across the antenna loading coil - from scratch
K7ITM wrote:
Another 'speriment occured to me, for those who think the coil current MUST be different at the two ends by the amount corresponding to the antenna section it replaces: try making the antenna diameter large compared with the coil diameter, say two to four times the coil diameter, while maintaining the same lengths, and see what happens. I suppose you'll have to adjust the inductance of the coil, but keep its diameter and length the same. If the current at the ends of the coil remains nominally the same as with a thin antenna, then I'll say you're onto something. If on the other hand, the current becomes much more similar at the two ends of the coil, that will be evidence of a different effect--in fact the effect that I expect is actually accounting for the difference. Perhaps someone would like to try that in NEC2 or NEC4 and share the results, if nobody is actually up to building the antenna and measuring things. I'm afraid that the proponents of the alternative theories aren't subject to either modeling or measurement results. There's already ample theoretical, modeling, and measurement evidence to show that the theory is faulty; further efforts would be a waste of time. Roy Lewallen, W7EL |
Current across the antenna loading coil - from scratch
Cecil Moore wrote:
Ian White GM3SEK wrote: Based entirely on what you yourself have written, I have told you that you don't understand something. Unless you can prove you are omniscient, Ian, the problem could possibly be with your misunderstanding of something, not mine. It certainly *is* possible to make a correct analysis of a short coil-loaded antenna in terms of forward, reflected and standing waves of current. My objections are only about errors in Cecil's specific attempt to do it. This particular problem is a small hole in our jigsaw puzzle of human knowledge. It would certainly be worthwhile to craft a new piece, and to have the satisfaction seeing it fit exactly into place. But jigsaw puzzles have unbreakable rules: a new piece must fit EXACTLY into the gap that it fills; and everywhere around its edges, the picture MUST join up EXACTLY. If it fails to fit exactly and in every detail, then it isn't the right piece. All the surrounding pieces of existing knowledge about antenna engineering fit neatly together to make a solid picture. We can see the big picture, and that we're only trying to fill a very small gap. That big picture is made up from only a very few primary colors. They can blend together to give infinite hues and subtleties, but everything comes from mixing those same few primary colors which DO NOT CHANGE. The 'primary colors' of antenna engineering are a few fundamental physical facts that DO NOT CHANGE from one piece of the puzzle to the next. (Out at the far edges of the puzzle, the advances of 20th-century physics have shown that classical physics is part of an even bigger picture than we'd imagined - but in doing so they have confirmed where the rules of classical physics still CAN be applied. That includes the whole of electrical and electronic engineering, except for what happens inside semiconductor devices. Regarding antennas, Einstein's equations include and clarify Maxwell's equations, and quantify the margins of error in this area of classical physics. This confirms that antenna engineering indeed CAN be completely and accurately understood using classical physics, because the margins of error are too small to affect any practical observations.) Returning to this particular gap in the picture of antenna engineering, concerning short loaded antennas, we can see that it's only a small gap. It is surrounded by large areas of existing knowledge that interlock solidly and completely. That means we can be confident there will be nothing different or special happening inside that gap. When trying to fill any gap in our existing knowledge, that piece of advance information - that the same fundamentals will apply - is a tremendous help. Or it should be... the trouble starts when someone tries to ignore that fact, or worse still, tries to fight it. It is also important to note that there are already several other ways of thinking about loaded antennas that DO fit perfectly into the puzzle. There are many alternative ways to think about any particular piece, and as long as they fit with reality all around them, they are interchangeable. Cecil wants to try a method based on forward, reflected and standing waves, and that's just fine. As i said, I'm sure it can be done. The existing knowledge that such a theory must fit includes: what travelling and standing waves are; what electric current is; what inductance does; how real-life coils are different; and how things change when circuits become physically large enough to make electromagnetic coupling important (so we begin to call them antennas). But Cecil's new piece for the puzzle uses new and special definitions and properties for electric current, inductance, and travelling and standing waves - they are not the same as in all the surrounding pieces. To me, that is absolute proof that his new piece doesn't fit. He has bent the rules to make it resemble the correct shape, but the colors don't match. Exactly why it doesn't fit remains a matter for debate. But I am fundamentally sure of the *fact* that it doesn't. (Will be away from the screen now until about Tuesday.) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current across the antenna loading coil - from scratch
K7ITM wrote:
Another 'speriment occured to me, for those who think the coil current MUST be different at the two ends by the amount corresponding to the antenna section it replaces: To the best of my knowledge, nobody believes that. The coil is much more efficient at the loading function than is the straight wire from which it is made. That's why inductive loading is more efficient than fractal antennas or other types of linear loading. -- 73, Cecil http://www.qsl.net/w5dxp |
Current across the antenna loading coil - from scratch
wrote in message
oups.com... Yuri Blanarovich wrote: W8JI and other unbelievers that antenna and loading coils can not be expressed in electrical degrees, can find another example in ON4UN's Low Band DXing book, 4th edition, page 9-47, Fig 9-58, showing loaded vertical with mast being 40 deg. 59.6 ft. long, loading coil of 144 uH taking (replacing radiator of) 40 deg and whip of 10 deg and 14.9 ft long, for overall 90 deg electrical and quarter wave resonant system. Soooo, to anyone outside of "equal current worshippers" it is obvious that coil is replacing 40 deg worth of radiator and it would drop equivalent amount of current across the coil that corresponds to the length of radiator that coil replaces, because rest of the "straight" radiator FORCES IT TO DO - because of standing wave and current. That is not correct Yuri. Anything from a pure inductance to a very poor distributed inductor (like a linear loading or stub) can be used and all would have different characteristics. "Pure inductance" - get me one, never subject of discussion here, about real antennas and real loading coils! A pure inductance would have no current difference at each end. A good compact inductor would have negligible current difference at each end, only a long straight wire would act like the "missing antenna". More BS, insisting on non-reality. One way to prove the coil does not replace missing length is to simply move the coil to a new location in a fixed height antenna. If the coil looked like 40 degrees, it would resonate the antenna no matter where it was installed. WRONG, read below, it's the required inductance/impedance and fixed "missing" degrees that need replacement. 73 Tom Another big WRONGO Tom! As we go deeper into the discussion and "arguments" from "unbelievers" and thanks to NM5K posting, about how fixed coil acts different, replaces different amount of degrees, it hit me that the reason is the impedance presented by the antenna (the straight part) radiator at the coil insertion point. Using just as example, radiator having 90 degrees at the resonance, with 50 degrees of whip and coil "replacing" 40 degrees in the said example from the book. You agree that impedance along the radiator changes, being low at the bottom, around tens of ohms, to being high at the top, around thousands of ohms. Now you place the loading coil along the radiator, one extreme being at the bottom, low impedance point - we know in order to maintain the resonance of say 13 ft high (long) radiator (90 electrical degrees at RESONANCE) the coil has a fewer turns, it's impedance is lower (as required by the lower impedance at the bottom end of the antenna), and current drop would relatively be small as W7EL proved and everybody knows. Now you move that coil say half way up the must, to higher impedance point at the antenna, and that coil now, in order to maintain the "match" has to have higher impedance, more turns and will exhibit MORE current drop across it, while replacing THE SAME NUMBER OF "missing" DEGREES AT THE RADIATOR. Assuming that our goal is to stay with the same physical length of the whip (which we do) and maintaining 90 degrees of resonant radiator. So the radiator stays 50 degrees ()+50, 10+40, 20+30, 30+20, 40 + 10) long and coil replaces the same "missing" 40 degrees. Same if you move the coil higher, higher antenna impedance point, more turns (inductance) required, more current drop exhibited, coil "replacing" THE SAME NUMBER OF 40 DEGREES. It needs more turns, but again, the coil's behavior is dictated by the impedance of the RADIATOR (standing waves) at the insertion point, dictating the inductance, number of turns of the coil in order to maintain the number of degrees, in order to maintain the resonance (90 degrees) of the radiator. In order to "overturn" this "Yuri's Theory" you would have to deny that resonant antenna has varying current across its radiator (wire) - to deny that current drops from the base to the tip. You would have to deny that coil in the RF circuit has varying impedance dependant on the number of turns and inductance and frequency. Deny that in order to maintain the resonant frequency of shortened radiator of the same physical length, you need to use coils of varying amount of turns depending on its insertion point along the radiator (less on the bottom, more closer to the top). That behavior of the coil is "FORCED" by the remaining "wires" in the radiator, in standing wave environment as Cecil is trying to get through with help of Kraus and others. So if the antenna is 50 degrees long and we want to maintain the resonance, the coil will replace (has to) the same 40 degrees regardless where it is placed, but its inductance and impedance will vary, depending on the impedance of the insertion point at the radiator. (Makes also sense - more turns - more current drop, RF choke effect. We are still talking RF current in standing wave antenna, not DC.) So the drop of RF current across the coil, depending on its position in the resonant quarter wave radiator can be from little at the base, to significant closer to the top, dependent on the position, insertion point, impedance of the radiator. This is much more significant cause of current drop across the coil that any "radiation or capacitance to the environment" (Tom's trying to "twist out of it") as is demonstrated by our arguments. So if we look at the fixed length of radiator and try to bring it to resonance with coils, placed at different locations along the radiator, we are replacing the SAME amount of electrical degrees, but depending on the required impedance, then the number of turns, or inductance has to be adjusted to conform. That jives what you and everybody knows and keep saying. So it is not the fixed inductance, (missing) length of wire in the coil, or same number of turns that replaces degrees of "missing" radiator, but the REQUIRED INDUCTANCE/IMPEDANCE and corresponding number of turns. I hope this makes it little bit more clear and shuts down another WRONGOOO that keeps popping up. Just measure it, stick it (properly defined) in EZNEC - IT IS ALL THERE, for everyone to see. So then if the standing wave causes drop of the RF current across the solid wire of the antenna, it also causes the drop of current across the loading coil, proportional to the amount of electrical degrees of radiator that coil "replaces", magnitude being dependent on the impedance and inductance required by the insertion point impedance along the radiator. (Almost sounds like "Yuri's Law" :-) I would like to thank NM5K for bringing it up and making me to understand what the "problem" and proof is. It made me realize what role impedance of the inductor plays in the STANDING WAVE antenna/circuit. Sooo! The coil can and have RF current variation, drop across it, just like piece of wire can, when in standing wave (antenna) environment. It is the major cause and not the whatever capacitance etc. You wanna call it K3BU's theory, I would be honored, but I do not claim any "ownership", many others before me showed that, directly or indirectly, including John Kraus, W8JK. I promise to do that article and series of experiments showing close correlation between measurements and proper modeling in EZNEC, just give me couple of weeks. I hope it will show and educate those willing to open their minds, and those "flat Earthers" can do what they choose to (look silly). I hope I made it more clear. I don't know how else I (we) can get it through! Soooo, but, but, but.... what? Yuri Blanarovich, K3BU.us I apologize to technical language purists for any clumsy wordiness' I may be guilty of. |
Current across the antenna loading coil - from scratch
Roy,
please see my other posting, otherwise, I really promise to do the step by step article, which will try to explain, correlate real life measurements and modeling and present the comprehensive case of current being different across antenna loading coils. Will do that with cooperation of other "defenders" that contributed to "our" cause. There is no point of going back and forth on tangents. We will measure, show the reality and then apply some theory, explanation and summary of what is going on. I hope it will correct misconceptions, provide better understanding and benefit in proper modeling and design of loaded antenna elements and systems. Otherwise, I think we have reached point, when it is pointless to go around in circles and argue that what IS, CAN'T BE, because..... Yuri, K3BU "Roy Lewallen" wrote in message ... Of course loading coils can be expressed in electrical degrees. But extrapolating this to mean that a loading coil has the same properties as an antenna with the same number of "degrees" has no justification. Yuri's theory was shown to be false not only by many of the good technical arguments given here in this thread, but also by a careful measurement I made over a year ago. I built a 33 foot high vertical and loaded it at the bottom with a toroidal inductor to resonate it at 3.8 MHz. The coil "replaced" 33.4 electrical degrees of antenna. Yuri's theory predicts that the current at the top of the inductor should be 16.5% less than that at the bottom, with a phase shift of 33.4 degrees. What I measured was a current drop of 5.4% and no measurable phase shift across the inductor. Both the description of the setup and the detailed results were posted on this newsgroup on Nov. 11, 2003, with the subject title " Current in antenna loading coils controversy - new measurement". Anyone can find those postings with groups.google.com. Yuri's response, also on Nov. 11, 2003 was to complain about my methodology, declare that he was still right, and state "I will measure things myself, try to verify previous measurements and then come up with conclusions and 'theory'." On Nov. 12, 2003, he posted: "I will be making snap-on current probe, which will make it easier to slide along the element and observe the current without the disturbance to the antenna and will be a bit different over the thermocouple meters. Just need a bit more time." Well, it's been over a year now, and all I've seen is the same unsupported theory with no evidence to contradict the contrary evidence which has been presented. When a belief stays fixed in spite of both contradictory solid theory and measurements, it fits into the category of religion, not science. So it's appropriate that Yuri speaks in terms of an explanation being a "heresy". What's next, "good" and "evil" theories? Roy Lewallen, W7EL Yuri Blanarovich wrote: W8JI and other unbelievers that antenna and loading coils can not be expressed in electrical degrees, can find another example in ON4UN's Low Band DXing book, 4th edition, page 9-47, Fig 9-58, showing loaded vertical with mast being 40 deg. 59.6 ft. long, loading coil of 144 uH taking (replacing radiator of) 40 deg and whip of 10 deg and 14.9 ft long, for overall 90 deg electrical and quarter wave resonant system. Soooo, to anyone outside of "equal current worshippers" it is obvious that coil is replacing 40 deg worth of radiator and it would drop equivalent amount of current across the coil that corresponds to the length of radiator that coil replaces, because rest of the "straight" radiator FORCES IT TO DO - because of standing wave and current. Such a heresy! Theeere is your sign! Yuri, K3BU/m |
Current across the antenna loading coil - from scratch
I fail to see what you are all arguing about.
A length of transmission line, or a coil insofar as it behaves as a length of transmission line, has a fixed number of degrees of phase shift which depends only on frequency. You can shift it about, put it in a different antenna, do what you like with it, but, at the same frequency, it will always have the same number of degrees. Now stop this childish argument before I bang your heads together. ---- Referee Reg. |
Current across the antenna loading coil - from scratch
"Roy Lewallen" wrote:
Of course loading coils can be expressed in electrical degrees. But extrapolating this to mean that a loading coil has the same properties as an antenna with the same number of "degrees" has no justification. I haven't heard anybody make that assertion in years. Coils occupy whatever number of degrees that they occupy. The technical fact is that standing wave current phase cannot be used as the method of measuring the number of degrees. The graphic at http://www.travstnd.GIF shows why. The standing wave current phase is unchanging unless the monopole length goes over 1/4WL. Here's what you said earlier: I said that Cecil's phase measurements agree with EZNEC (and generally accepted theory) -- there should be almost no phase shift in the current along the wire. If there's no phase shift along the wire, why would you expect to measure phase shift through a coil. After you made the above posting, I thought you understood that - but apparently not. I told you that your phase shift measurement was invalid a year ago and it is just as invalid now as it was then. There is no phase information contained in standing wave current phase. This is the basic misconception that has resulted in invalid data reported by you. What I measured was a current drop of 5.4% and no measurable phase shift across the inductor. But Roy, you used standing wave current phase to try to measure the phase shift across the inductor. The standing wave current phase is known to be unchanging in a wire. Why would you expect it to change through a coil? As Gene Fuller says, the only phase information in the standing wave current is in the magnitude measurement. If the magnitude changed by 5.4%, the phase shift was roughly arc-cos(1 - 0.054) = arc-cos(0.946) = ~19 degrees. Please take a look at what EZNEC says about the standing wave phase shift in 1/4WL of wire at: http://www.qsl.net/w5dxp/travstnd.GIF and please tell us again how you used a current with an unchanging flat phase to try to measure the phase shift through a coil. Well, it's been over a year now, and all I've seen is the same unsupported theory with no evidence to contradict the contrary evidence which has been presented. No evidence? Even EZNEC says one cannot use standing wave current phase to measure phase shift. I told you that fact over a year ago. Your phase measurement methods are just as invalid today as they were a year ago. When a belief stays fixed in spite of both contradictory solid theory and measurements, it fits into the category of religion, not science. You are talking about your religious method of using the unchanging standing wave current phase to try to measure a phase shift. EZNEC says that is not a valid approach. Even Gene Fuller says there is zero phase information in standing wave current wave and he generally agrees with you. Regarding the cos(kz)*cos(wt) term in a standing wave: Gene Fuller, W4SZ wrote: In a standing wave antenna problem, such as the one you describe, there is no remaining phase information. Any specific phase characteristics of the traveling waves died out when the startup transients died out. Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. -- 73, Cecil http://www.qsl.net/w5dxp |
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